This invention relates to a plastic optical fiber cable with a ferrule adapted to connect an optical fiber cable through a connector to an optical device or to connect several optical fiber cables to each other.
When an optical fiber cable is connected to an optical device or optical fiber cables are connected to each other through a connector, it is in general the practice to mount a ferrule for reinforcing the end of the cable.
The ferrule is mounted when the core of the optical fiber cable is formed as a quartz optical fiber and a plastic optical fiber.
The plastic optical fiber cable is formed of a plastic optical fiber and a plastic sheath covering the outer periphery of the core in a manner known per se, and the ferrule mounted at the end of the cable is formed of plastic or metal or of a combination of plastic and metal.
A conventional example of mounting a plastic ferrule on the outer periphery of the end of the plastic optical fiber cable will be described.
The plastic sheath is first stripped at the end of the plastic optical fiber cable for a suitable length, thereby exposing the optical fiber core from the end of the cable.
Then, an adhesive is coated on the exposed part of the optical fiber cable, a plastic ferrule is engaged with the outer periphery of the part coated with the adhesive, and a clamping ring engaged with the outer periphery of the base end side of the ferrule is crimped to secure the ferrule to the end of the optical fiber cable.
Subsequently, the optical fiber cable is kept intact until the adhesive is cured. After the adhesive is cured, the end of the optical fiber cable with the ferrule is polished so that the end face of the ferrule and the end face of the optical fiber are disposed in the same plane.
On the other hand, when a ferrule formed of metal is mounted at the end of the plastic optical fiber cable, the metal ferrule and the plastic sheath may be crimped, but the metal ferrule cannot be crimped directly to the bare plastic optical fiber due to a danger to damage of the core. Therefore, the adhesive is employed in case of securing the plastic optical fiber to the metal ferrule.
Further, when the front half (terminal end) of the ferrule is formed of plastic and the rear half (base end) of the ferrule is formed of metal in combination, the terminal end of the plastic optical fiber is secured to the front half (formed of plastic) of the ferrule via an adhesive, and the terminal end of the plastic sheath and the rear half (formed of metal) of the ferrule are crimped.
In addition, the prior art of mounting a ferrule at the end of an optical fiber cable having an optical fiber core is disclosed in U.S. Pat. Nos. 4,178,063 and 4,362,356. In the U.S. patents, the ferrule is mounted at the end of the optical fiber core mainly by an adhesive or by adhesive and a clamping ring.
However, securing the ferrule to the end of the plastic optical fiber cable mainly by an adhesive takes a considerable period of time to cure the adhesive, thereby decreasing the finishing efficiency.
Further, when the clamping ring is employed as means for temporarily fastening the ferrule until the adhesive is cured, the efficiency cannot be improved due to the use of the adhesive. In addition, crimping means for indirectly crimping the clamping ring from above the ferrule provides only a weak securing force between the ferrule and the plastic optical fiber,
and is not a highly reliable fastening means.
These problems arise in the ferrule mounting means which employ the adhesive irrespective of the material of the ferrule.
In view of the above-described drawbacks, plastic is desired as the ferrule for a plastic optical fiber cable, but in the case of the conventional practice which depends upon an adhesive as the means for securing the ferrule, its workability and fastening strength are not satisfactory.